A secretive Chinese military unit is believed to be behind a prolific series of hacking attacks, according to a top US computer security company.

A report by Mandiant claims that the People's Liberation Army's Shanghai-based Unit 61398 is the most likely driving force behind the hacking.

Mandiant said the unit had carried out "sustained" attacks on a wide set of industries.

The report said that the nature of 'Unit 61398's' work is considered by China to be a state secret and many in the government do not even know what it is up to. We guess this makes plausible denial, more, er, plausible.

According to the Washington Post, Mandiant said it was time to acknowledge the threat is originating in China, and the company wanted to do its part to arm and prepare security professionals to combat the threat effectively.

Unit 61398, which is also known online as the "comment crew," is located in Shanghai's Pudong district, China's financial and banking hub. It is staffed by perhaps thousands of people proficient in English as well as computer programming and network operations.

So far the outfit has allegedly pinched "hundreds of terabytes of data from at least 141 organizations across a diverse set of industries beginning as early as 2006", the report said.

Most of the victims were located in the United States, with smaller numbers in Canada and Britain. They have picked up details of mergers and acquisitions and monitored the emails of senior employees.

The Chinese government has consistently denied being involved in such activities.